Method, system and device for playing enterprise color ringback tone

ABSTRACT

A method for playing an enterprise color ringback tone is disclosed, including the following steps: establishing, by a service switching entity, a connection with a service access entity in accordance with an EVC access code; searching, by the service access entity, for a connection identifier of a destination terminal corresponding to a service identifier of the destination terminal in accordance with a correspondence relationship between the service identifier and the connection identifier of the terminal, and sending the connection identifier of the destination terminal to the service switching entity; and establishing, by the service switching entity, a connection between the source terminal and the destination terminal in accordance with the connection identifier of the destination terminal, and playing, by the service access entity, an enterprise CRBT to the source terminal. A system and a device for playing an enterprise color ringback tone are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2007/003023, filed on Oct. 22, 2007, which claims priority toChinese patent application No. 200710002484.3, filed on Jan. 29, 2007;both of which are incorporated by reference herein their entireties.

FIELD OF THE INVENTION

The present invention relates to data transmission techniques in thefield of communications, and in particular, to a method, a system and adevice for playing an enterprise color ringback tone.

BACKGROUND OF THE INVENTION

Nowadays, more and more companies and organizations employ theEnterprise Virtual Centrex (EVC) service. These enterprise clientspublish one EVC number to the public, and both internal users andexternal users of the enterprise can enjoy services provided by the EVC.For example, by dialing an access number of the EVC, a calling party canget various services such as manual forwarding, automatic forwarding,voice forwarding, and switchboard outwards calling. Manual forwardingrefers to the service provided by an operator, with which calls areforwarded by the operator to a called party after inquiry; automaticforwarding means that the calling party directly dials a normal numberof the called party, and the system establishes a connection between thecalling party and the called party according to the normal number; voiceforwarding is that the calling party speaks out another identifier ofthe called party, for example a name, via a voice system, and the systemfinds the number of the called party and establishes a sessionconnection; and EVC outwards calling means that an enterprise membercalls an external user of the enterprise through the switchboard, whichmay reduce communication cost for business.

Different from existing Color RingBack Tone (CRBT) services, theenterprise CRBT service can provide a CRBT customized for all internalusers of the enterprise, without affecting personal CRBTs of theinternal users, and can be customized according to time periods,departments or enterprises.

Mainly, there are two existing methods for implementing the enterpriseCRBT service. FIG. 1 illustrates a flow chart of the first method, inwhich terminal A refers to a calling terminal, terminal B refers to acalled terminal, a soft switching entity (SOFTX)/Service Switching Point(SSP) serving the terminal A is denoted as SOFTX/SSP(a), and anSOFTX/SSP serving the called terminal is denoted as SOFTX/SSP(b). Themethod generally includes the following steps.

Step 101: Terminal A sends to SOFTX/SSP(a) a call request, includingtelephone number information of terminal B which has subscribed for theenterprise CRBT service.

Step 102: Upon reception of the call request, SOFTX/SSP(a) sends to aService Control Point (SCP) in an intelligence network an initialmessage (IDP), including telephone number information of terminal A andterminal B.

Step 103: The SCP determines that terminal B has subscribed for theenterprise CRBT service based on the telephone number information ofterminal B, and sends to SOFTX/SSP(a) a CONNECT message including thetelephone number information of terminal B and a routing code for acorresponding CRBT.

Step 104: If SOFTX/SSP(a) receives the CONNECT message and determinesthat the message also includes a resonant CRBT call identifier, whichindicates the use of SSP resonance technology in this method forimplementing the enterprise CRBT service, then SOFTX/SSP(a) sends toSOFTX/SSP(b) an Initial Address Message (IAM), including the telephonenumber information of terminal B requesting for a connection betweenterminal A and terminal B while blocking a ringback tone from terminalB. SOFTX/SSP(b) returns to SOFTX/SSP(a) an Address Complete Message(ACM) indicating the success of establishing the connection. ThenSOFTX/SSP(a) sends to a CRBT Advanced Intelligence Peripheral (AIP) anIAM message including the CRBT routing code and establishes a connectionwith the CRBT AIP, then the CRBT AIP returns an ACM message toSOFTX/SSP(a), and therefore an enterprise CRBT played by the CRBT AIPcan be heard at terminal A.

Step 105: An answer message (ANM) is sent to SOFTX/SSP(b) as soon asterminal B is off-hook.

Step 106: Upon reception of the ANM message, SOFTX/SSP(b) sends to theSCP an IDP message reporting the off-hook event of terminal B.

Step 107: Upon reception of the IDP message, the SCP sends toSOFTX/SSP(a) a release message (REL) instructing SOFTX/SSP(a) to teardown the connection to the CRBT AIP to stop the playing of theenterprise CRBT, meanwhile terminal A and terminal B start tocommunicate.

In the method illustrated by FIG. 1, different subsystems have to beused to implement the CRBT service and switchboard service;consequently, corresponding data have to be stored in both of thesubsystems in order to implement the enterprise CRBT service, whichincreases data redundancy. In addition, this method is only applicablein a wired communication network.

The second existing method for implementing the enterprise CRBT serviceis illustrated in FIG. 2, where terminal A also refers to a callingterminal, terminal B also refers to a called terminal, and an SSP/MobileSwitching Center (MSC)/Gateway Mobile Switching Center (GMSC) servingterminal A is denoted as GMSC/MSC/SSP(a), and a GMSC/MSC/SSP serving thecalled terminal is denoted as GMSC/MSC/SSP(b). The method generallyincludes the following steps.

Step 201: Terminal A sends to GMSC/MSC/SSP(a) a call request including atelephone number of terminal B which has subscribed for the enterpriseCRBT service. If terminal A is a fixed line user or a user of othermobile networks, the GSMC looks up subscription information of terminalB (T-CSI) in a Home Location Register (HLR); and if terminal A is alocal user, the MSC looks up the T-CSI information in an HLR.

Step 202: According to the T_CSI information, GMSC/MSC/SSP(a) sends toan SCP, to which terminal B is homed, an IDP message including thetelephone number information of terminal A and terminal B.

Step 203: The SCP issues a Request Report Basic call state model Event(RRBE) to GMSC/MSC/SSP(a), instructing GMSC/MSC/SSP(a) to report linkconnection status in real time.

Step 204: The SCP sends a CONNECT message to GMSC/MSC/SSP(a) to instructGMSC/MSC/SSP(a) to establish a connection to a CRBT AIP, including thetelephone number of terminal B and a CRBT routing code, and a roamingnumber of terminal B if terminals A and terminal B are terminals indifferent networks.

Step 205: Upon reception of the CONNECT message, GMSC/MSC/SSP(a) routesthe call request to the CRBT AIP, the CRBT AIP furthers connects thecall to GMSC/MSC/SSP(b), and finally GMSC/MSC/SSP(b) connects the callto terminal B.

Step 206: The CRBT AIP plays an enterprise CRBT customized by the callednumber to terminal A while blocking a ringback tone played from terminalB. When terminal B is off-hook, the switchboard CRBT AIP detects theoccurrence of the event and stops playing the enterprise CRBT, andterminal A and terminal B can start to communicate. The connectionbetween GMSC/MSC/SSP(a) and the CRBT AIP is interrupted if thecommunication ends.

In the method illustrated by FIG. 2, as terminal B is called via theCRBT AIP, the trunk link between the CRBT AIP and GMSC/MSC/SSP(a) isstill occupied after the session between terminals A and B is enabled.Such a state will last until the communication between terminals A andterminal B ends, which may result in reduplicate links in implementationof the CRBT service, wastes trunk equipments, and thus degrades theparallel processing capability of the color AIP for CRBT service. Inaddition, during the call, the calling terminal is connected to thecalled terminal directly through the telephone number of the calledterminal; consequently, only users of an enterprise within the samenetwork can join the enterprise CRBT, which may limit terminals used bythe users of the enterprise and cannot meet individualized requirementsof the users in the enterprise.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a method, a system and a device forplaying an enterprise CRBT, in order to address the problems in theconventional art such as reduplicate links, data redundancy and theoccupancy of a lot of trunk link resources. The method includes thesteps of:

receiving, by a service switching entity, a call request including anEVC access code sent by a source terminal, and establishing a connectionwith a service access entity according to the EVC access code;

receiving, by the service access entity, a service identifier of adestination terminal sent by the source terminal, searching for aconnection identifier of the destination terminal corresponding to theservice identifier of the destination terminal according to acorrespondence relationship between the service identifier and theconnection identifier of the destination terminal, and sending theconnection identifier of the destination terminal to the serviceswitching entity; and

establishing, by the service switching entity, a connection between thesource terminal and the destination terminal according to the connectionidentifier of the destination terminal, and playing, by the serviceaccess entity, an enterprise CRBT to the source terminal.

An embodiment of the invention further provides a system for playing anenterprise CRBT, which includes a service switching entity and a serviceaccess entity, wherein:

the service access entity includes:

a first reception unit, adapted to receive a service identifier of adestination terminal sent by a source terminal;

a search unit, adapted to search a connection identifier correspondingto the service identifier of the destination terminal according to acorrespondence relationship between the service identifier and theconnection identifier of the terminal, and send the connectionidentifier of the destination terminal to the service switching entity;and

a play unit, adapted to play an enterprise CRBT to the source terminal;

and

the service switching entity includes:

a second reception unit, adapted to receive a call request including anEVC access code sent by the source terminal, and the connectionidentifier of the destination terminal sent by the service accessentity;

a first connection unit, adapted to establish a connection with theservice access entity according to the EVC access code; and

a second connection unit, adapted to establish a connection between thesource terminal and the destination terminal according to the connectionidentifier of the destination terminal.

An embodiment of the invention further provides a service switchingentity including:

a reception unit, adapted to receive a call request including an EVCaccess code sent by a source terminal, and a connection identifier of adestination terminal sent by a service access entity;

a first connection unit, adapted to establish a connection with theservice access entity according to the EVC access code; and

a second connection unit, adapted to establish a connection between thesource terminal and the destination terminal according to the connectionidentifier of the destination terminal.

According to the embodiments of the invention, first the serviceswitching entity establishes the connection with the service accessentity according to the EVC access code, and the service access entitysearches for the connection identifier corresponding to the serviceidentifier of the destination terminal according to a storedcorrespondence relationship between the service identifier and theconnection identifier of the terminal, and sends the connectionidentifier of the destination terminal to the service switching entity;then the service switching entity establishes the connection between thesource terminal and the destination terminal according to the connectionidentifier of the destination terminal, and the service access entityplays the enterprise CRBT to the source terminal; and finally theservice access entity disconnects the connection with the service accessentity when the destination terminal answers. Therefore, the problem ofreduplicate links in playing of the enterprise CRBT is avoided, trunklink resources are saved and data redundancy is reduced. Because theenterprise CRBT service is deployed directly at the service accessentity side, maintenance operations are simplified, time of the callprocess is shortened, system burden is reduced, and different networkterminals can join the enterprise CRBT, therefore individualizedrequirements of users in the enterprise are met.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the first method for implementing theenterprise CRBT service in the conventional art;

FIG. 2 is a flow chart of the second method for implementing theenterprise CRBT service in the conventional art;

FIG. 3 is a structural diagram of a system for playing an enterpriseCRBT according to an embodiment of the present invention;

FIG. 4 is a flow chart of a method for playing an enterprise CRBTaccording to an embodiment of the present invention; and

FIG. 5 is a structural diagram of a service switching entity accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the invention are applied in a system including aservice switching entity, a service access entity and at least twoterminals. First, a source terminal sends to the service switchingentity a call request including an EVC access code, the serviceswitching entity establishes a connection with the service access entityaccording to the EVC access code; then the source terminal sends aservice identifier of a destination terminal to the service accessentity, and the service entity searches for a connection identifiercorresponding to the service identifier of the destination terminalaccording to a stored correspondence relationship between the serviceidentifier and the connection identifier of the terminal and sends theconnection identifier of the destination terminal to the serviceswitching entity; next the service switching entity establishes aconnection between the source terminal and the destination terminalaccording to the connection identifier of the destination terminal, andthe service access entity plays a stored enterprise CRBT to the sourceterminal; finally, when the destination terminal answers, the serviceswitching entity disconnects the connection with the service accessentity. Therefore, a procedure for playing the enterprise CRBT to thesource terminal is accomplished through the above steps. In anembodiment of the invention, the service switching entity can be anentity such as tandem office switch (MS)/MSC/GMSC, and the serviceaccess entity can be an entity such as switchboard AIP. Further, in anembodiment of the invention, a service control entity can be appliedwhich may include an entity such as SCP.

The method of the invention will be described in details below withreference to the drawings.

FIG. 3 illustrates a structural diagram of a system for playing anenterprise CRBT according to an embodiment of the present invention. Thesystem includes a service switching entity and a service access entity.Particularly, the service access entity includes a first reception unit11, a search unit 12 and a play unit 13. The first reception unit 11 isadapted to receive a service identifier of a destination terminal sentby a source terminal. The search unit 12 is adapted to search for aconnection identifier corresponding to the service identifier of thedestination terminal according to a correspondence relationship betweenthe service identifier and the connection identifier of the terminal andsend the connection identifier of the destination terminal to theservice switching entity. The play unit 13 is adapted to play anenterprise CRBT to the source terminal.

The service switching entity includes a second reception unit 21, afirst connection unit 22 and a second connection unit 23. The secondreception unit 21 is adapted to receive a call request including an EVCaccess code sent by the source terminal, and the connection identifierof the destination terminal sent by the service access entity. The firstconnection unit 22 is adapted to establish a connection with the serviceaccess entity according to the EVC access code. The second connectionunit 23 is adapted to establish a connection between the source terminaland the destination terminal according to the connection identifier ofthe destination terminal.

The system can include a service control entity which includes a firstcontrol unit 31 adapted to control the service switching entity todisconnect the connection with the service access entity when thedestination terminal answers.

The service control entity can further include a second control unit 32adapted to control the service switching entity to establish theconnection with the service access entity upon reception of the callrequest including the EVC access code sent by the service switchingentity. Then the service switching entity can include a sending unit 24adapted to send the call request to the second control unit 32.

The service switching entity can include a disconnection unit 25 adaptedto disconnect the connection with the service access entity afterreceiving the connection identifier of the destination terminal andbefore establishing the connection between the source terminal and thedestination terminal. Furthermore, the service switching entity caninclude a third connection unit 26 adapted to establish the connectionwith the service access entity after establishing the connection betweenthe source terminal and the destination terminal and before the serviceaccess entity plays the stored enterprise CRBT to the source terminal.

The inventive method will be described in details below with referenceto an embodiment. FIG. 4 illustrates a flow chart of a method forplaying an enterprise CRBT according to an embodiment of the invention,in which MS/MSC refers to a service switching entity, terminal A refersto a source terminal, terminal B refers to a destination terminal,MS/MSC(a) refers to a service switching entity serving terminal A,MS/MSC(b) refers to a service switching entity serving terminal B, SCPrefers to a service control entity, and switchboard AIP refers to aservice access entity. The method includes the following steps.

Step 401: Terminal A sends to MS/MSC(a) a call request including an EVCaccess code, and MS/MSC(a) establishes a connection with the switchboardAIP according to the EVC access code.

In this step, terminal A first sends to MS/MSC(a) the call requestincluding information of the EVC access code. In this embodiment, it canbe assumed that the procedure of sending the call request isaccomplished in a way that terminal A dials the EVC access code and thecall is switched to MS/MSC(a). Upon reception of the call request,MS/MSC(a) determines whether terminal A is a mobile network device or afixed network device. If terminal A is a mobile network device,MS/MSC(a) obtains T_CSI information of the EVC access code by sendingrouting information (SRI) including the EVC access code to an HLR; andif terminal A is a fixed network device, MS/MSC(a) obtains the T_CSIinformation of the EVC access code by sending routing information (SRI)including the EVC access code to a smart home location register (SHLR).

In this embodiment, MS/MSC(a) sends a trigger signal to the SCP uponreception of the SRI information of the EVC access code, and the SCPcontrols MS/MSC(a) to establish a connection with the switchboard AIP.Particularly, SSP(a) at the MS/MSC(a) side sends a DIP message includingthe EVC access code information as the trigger signal to the SCP. Uponreception of the IDP message, the SCP determines that the EVC service isto be implemented according to the EVC access code information in themessage, and issues an RRBE message to MS/MSC(a) for real timemonitoring of the link connection status. An establish temporaryconnection (ETC) message including routing information of theswitchboard AIP is also issued to instruct MS/MSC(a) to establish theconnection with the switchboard AIP. Thus, MS/MSC(a) sends to theswitchboard AIP an IAM message including the routing information of theswitchboard AIP and establishes the connection between them.

After the connection is established, the switchboard AIP sends anauxiliary request instruction (ARI) message to the SCP, by which aconnection with the SCP is established, and thereafter the SCP sends tothe switchboard AIP a user interaction script run UIScriptrun messageinstructing the switchboard AIP to start a switchboard service flow.

Step 402: Terminal A sends a service identifier of terminal B to theswitchboard AIP, and the switchboard AIP searches for a connectionidentifier of terminal B according to a stored correspondencerelationship between the service identifier and the connectionidentifier of the terminal and sends the connection identifier toMS/MSC(a).

After MS/MSC(a) establishes the connection with the switchboard AIP,i.e. terminal A establishes a session connection with the switchboardAIP through MS/MSC(a), the service identifier of terminal B is sent tothe switchboard AIP. In this invention, the service identifier is anidentifier, which can indicate the identity of terminal B, for example,a name identifier of terminal B, other than the connection identifier.For example, if the switchboard AIP provides terminal A with a manualservice, terminal A speaks out the name of terminal B, i.e. name of theuser, then an operator can obtain connection information of terminal Bby looking up the pre-stored correspondence relationship between theservice identifier and the connection identifier of the terminal. Inthis embodiment, the connection identifier is a telephone number. Afterobtaining telephone number information of terminal B, the switchboardAIP sends the information to MS/MSC(a), and in this embodiment, theswitchboard AIP reports the telephone number information of terminal Bby sending a user interaction script event (UIScriptEvent) message tothe SCP. After obtaining the telephone number information of terminal B,the SCP sends to MS/MSC(a) a CONNECT message including the telephonenumber of terminal B. In order to achieve no reduplicate links in thecall forwarding, MS/MSC(a) needs to disconnect the connection with theswitchboard AIP after obtaining the telephone number of terminal B, Andin this embodiment, the disconnection step can be as follows: uponreception of the telephone number of terminal B reported by theswitchboard AIP, the SCP determines that terminal B has subscribed forthe enterprise CRBT service and sends a user interaction script close(UIScriptClose) message to the switchboard AIP to release the connectionwith the switchboard AIP. Also the SCP sends to MS/MSC(a) a DisconnectForward Connection (DFC) message instructing MS/MSC(a) to tear down thetemporary session connection with the switchboard AIP, then MS/MSC(a)sends a REL message to the switchboard AIP and disconnects theconnection between them.

Step 403: MS/MSC(a) establishes the connection between terminal A andterminal B according to the telephone number information of terminal B,and the switchboard AIP plays an enterprise CRBT to terminal A.

After obtaining the telephone number information of terminal B,MS/MSC(a) establishes the connection between terminal A and terminal Baccording to the telephone number information. Apparently, MS/MSC(a) canalso disconnect the connection with the switchboard AIP afterestablishing the connection between terminal A and terminal B accordingto the obtained telephone number information of terminal B.

Next, the SCP sends a request report basic call state model event (RRBE)and an application charging (AC) message to MS/MSC(a), instructingMS/MSC(a) to monitor in real time events at the terminal such asoff-hook, no-answer, routing selection failure and report a billingreport.

In the above step 402, the CONNECT message sent by the SCP furtherincludes a CRBT routing identifier, an EVC access code and a CRBT accessidentifier. Particularly, the CRBT routing identifier and the EVC accesscode are used to instruct MS/MSC(a) to connect the call to theswitchboard AIP, so that the switchboard AIP can play an enterprise CRBTto terminal A. The CRBT access code and the telephone number of terminalB are used to notify the HLR that the CRBT service has been triggeredand do not trigger the CRBT service for terminal B again, therebyavoiding repetitions. Specifically, upon reception of the CONNECTmessage, MS/MSC(a) sends to MS/MSC(b) an IAM message including thetelephone number of terminal B and the CRBT access code, and MS/MSC(b)further sends the CRBT access code to the HLR at the destination endinstructing the HLR not to trigger the CRBT service for terminal B againaccording to the CRBT access code, and sends an ACM message toMS/MSC(a). Thereafter MS/MSC(a) establishes the connection with theswitchboard AIP through an IAM message according to the obtained EVCaccess code. If the switchboard AIP stores more than one enterpriseCRBTs, MS/MSC(a) sends the CRBT routing identifier to the switchboardAIP, and the switchboard AIP finds one of the enterprise CRBTscorresponding to the CRBT routing identifier according to acorrespondence relationship between the CRBT routing identifier and theenterprise CRBT, returns an ACM message to MS/MSC(a), and triggers aplay process for the enterprise CRBT to play stored audio data toterminal A.

Step 404: When terminal B answers, the SCP controls MS/MSC(a) todisconnect the connection with the switchboard AIP.

When the terminal B is off-hook, i.e. an off-hook message is sent toMS/MSC(b), the SSP(b) at the MS/MSC(b) side reports an off-hook messageof terminal B to the SCP. Upon reception of the message, the SCP sends aREL message to MS/MSC(a) to control MS/MSC(a) to disconnect theconnection with the telephone AIP. Upon reception of the REL message,MS/MSC(a) sends a REL message to the switchboard AIP and disconnects theconnection with the switchboard AIP, then the switchboard stops playingthe enterprise CRBT to terminal A, and terminals A and B start tocommunicate.

With the above detailed descriptions of the method and the system of thepresent invention, an embodiment of the present invention furtherprovides a service switching entity as illustrated in FIG. 5, which isapplicable in a system including a service access entity and at leasttwo terminals. The service switching entity includes a reception unit41, a first connection unit 42 and a second connection unit 43. Thereception unit 41 is adapted to receive a call request including an EVCaccess code sent by a source terminal, and a connection identifier of adestination terminal sent by the service access entity. The firstconnection unit 42 is adapted to establish a connection with the serviceaccess entity according to the EVC access code. The second connectionunit 43 is adapted to establish a connection between the source terminaland the destination terminal according to the connection identifier ofthe destination terminal.

The service switching entity can include a first disconnection unit 44adapted to disconnect the connection with the service access entityafter receiving the connection identifier of the destination terminaland before establishing the connection between the source terminal andthe destination terminal. The service switching entity can include athird connection unit 45 adapted to establish the connection with theservice access entity after establishing the connection between thesource terminal and the destination terminal and before the serviceaccess entity plays a stored enterprise CRBT to the source terminal.

The service switching entity can further include a second disconnectionunit 46 adapted to disconnect the connection with the service accessentity when the destination terminal answers.

With the present invention, playing of enterprise CRBTs can be realizedin both wired communication network and wireless communication networkswithout reduplicate links, and the enterprise CRBT service can beimplemented at the service access entity side, which simplifiesmaintenance operations and reduces system burden, therefore a callingparty can hear an enterprise CRBT when dialing an EVC access code andhear a personal CRBT of an enterprise member when directly dialing aninternal user of an enterprise.

Evidently, those skilled in the art may make modifications andvariations of the invention without departing from the scope of theinvention. Accordingly, the invention is intended to include thesemodifications and variations provided that they come into the scope ofthe claims appended to the invention and equivalents thereof.

What is claimed is:
 1. A method for playing an enterprise Color RingBackTone, CRBT, comprising: receiving, by a service switching entity, a callrequest comprising an Enterprise Virtual Centrex, EVC, access code sentby a source terminal, and establishing a connection with a serviceaccess entity in accordance with the EVC access code; receiving, by theservice access entity, a service identifier of a destination terminalsent by the source terminal, searching for a connection identifier ofthe destination terminal corresponding to the service identifier of thedestination terminal in accordance with a correspondence relationshipbetween the service identifier and the connection identifier of thedestination terminal, and sending the connection identifier of thedestination terminal to the service switching entity; and after theservice access entity sends the connection identifier of the destinationterminal to the service witching entity and before the service switchingentity establishes the connection between the source terminal and thedestination terminal in accordance with the connection identifier of thedestination terminal the method comprises: disconnecting by the serviceswitching entity the connection with the service access entity; andafter the service switching entity establishes the connection betweenthe source terminal and the destination terminal in accordance with theconnection identifier of the destination terminal and before the serviceaccess entity plays the enterprise CRBT to the source terminal themethod further comprises: establishing by the service switching entitythe connection with the service access entity; and playing, by theservice access entity, an enterprise CRBT to the source terminal.
 2. Themethod according to claim 1, further comprising: controlling, by aservice control entity, the service switching entity to disconnect theconnection with the service access entity when the destination terminalanswers.
 3. The method according to claim 1, wherein the step of theestablishing, by the service switching entity, the connection with theservice access entity in accordance with the EVC access code comprises:sending, by the service switching entity, a trigger signal to a servicecontrol entity in accordance with the EVC access code; and controlling,by the service control entity, the service switching entity to establishthe connection with the service access entity.
 4. The method accordingto claim 3, wherein the step of controlling, by the service controlentity, the service switching entity to establish the connection withthe service access entity comprises: sending, by the service controlentity, to the service switching entity an Establish TemporaryConnection message comprising routing information of the service accessentity; and establishing, by the service switching entity, theconnection with the service access entity in accordance with the routinginformation.
 5. The method according to claim 1, wherein a servicecontrol entity controls the service switching entity to disconnect theconnection with the service access entity.
 6. The method according toclaim 1, wherein a service control entity controls the service switchingentity to establish the connection with the service access entity. 7.The method according to claim 5, wherein the step of the service controlentity controlling the service switching entity to disconnect theconnection with the service access entity comprises: sending, by theservice control entity, a Disconnect Forward Connection message to theservice switching entity; and sending, by the service switching entity,a release message to the service access entity to disconnect theconnection.
 8. The method according to claim 6, wherein the step of theservice control entity controlling the service switching entity toestablish the connection with the service access entity comprises:sending, by the service control entity, to the service switching entitya connection message comprising the EVC access code; and establishing,by the service switching entity, the connection with the service accessentity in accordance with the EVC access code.
 9. The method accordingto claim 8, wherein if the service access entity stores more than oneenterprise CRBTs, the connection message further comprises a CRBTrouting identifier, the service switching entity sends the CRBT routingidentifier to the service access entity, and the service access entitysearches for an enterprise CRBT corresponding to the CRBT routingidentifier in accordance with a correspondence relationship between theCRBT routing identifier and the enterprise CRBT.
 10. The methodaccording to claim 8, wherein the connection message further comprises aCRBT access identifier, and the service switching entity sends the CRBTaccess identifier to a home location entity of the destination terminal,instructing the home location entity not to trigger a CRBT service forthe destination terminal.
 11. The method according to claim 1, whereinthe step of sending the connection identifier of the destinationterminal to the service switching entity comprises: sending, by theservice access entity, the connection identifier of the destinationterminal to a service control entity; and sending, by the servicecontrol entity, the connection identifier of the destination terminal tothe service switching entity.
 12. A system for playing an enterprisecolor ringback tone, CRBT, comprising a service switching entity and aservice access entity, wherein: the service access entity comprises: afirst reception unit, adapted to receive a service identifier of adestination terminal sent by a source terminal; a search unit, adaptedto search a connection identifier corresponding to the serviceidentifier of the destination terminal in accordance with acorrespondence relationship between the service identifier and theconnection identifier of the terminal, and to send the connectionidentifier of the destination terminal to the service switching entity;and a play unit adapted to play an enterprise CRBT to the sourceterminal; and the service switching entity comprises: a second receptionunit, adapted to receive a call request comprising an Enterprise VirtualCentrex, EVC, access code sent by the source terminal, and theconnection identifier of the destination terminal by the service accessentity; a first connection unit, adapted to establish a connection withthe service access entity in accordance with the EVC access code; and asecond connection unit, adapted to establish a connection between thesource terminal and the destination terminal in accordance with theconnection identifier of the destination terminal a disconnection unitadapted to disconnect the connection with the service access entityafter receiving the connection identifier of the destination terminaland before establishing the connection between the source terminal andthe destination terminal; and a third connection unit adapted toestablish the connection with the service access entity afterestablishing the connection between the source terminal and thedestination terminal and before the service access entity plays theenterprise CRBT to the source terminal.
 13. The system according toclaim 12, further comprising a service control entity, wherein theservice control entity comprises a first control unit, adapted tocontrol the service switching entity to disconnect the connection withthe service access entity when the destination terminal answers.